@david999 😀

Posted by: @david999

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@toodles yup I can feel the sensor inside so likely ok. Have swung a camera around to watch how it manages the ice. At 76 it’s nice that you keep an interest in these things, I’m 66 an engineer and still learning new stuff but it keeps you alive I say. 😊

The actual temperature sensor is near the end of the black outer sheath, and the cable tie is probably to stop the outer sheath from moving. See the attached.

https://uk.rs-online.com/web/p/thermistors/1241081?cm_mmc=UK-PLA-DS3A-_-google-_-CSS_UK_EN_PMAX_Catch+All-_--_-1241081&matchtype=&&gad_source=1&gclid=Cj0KCQjwqpSwBhClARIsADlZ_TlL3rRUlR86xtqYXMhsvA6O9-HHgxCSZW5iqPu8_dA1rO_XLs5Mdu4aAqpzEALw_wcB&gclsrc=aw.ds

@derek-m may I ask another question please.  Where is the best place for the room stat and the radiator with no stat on it, the bypass I think they call it. At the moment the bypass is in the hall with the room stat but that leaves all of one area cold the bedroom, bathroom, dining room. since the hall is the warmest area because we have two rads there, three in the living room and a log burner, the kitchen with two and no door and a bathroom in the hall with one. We moved the room stat to the area that was cold but that bypass rad in the hall is making it too warm. Should it be moved to the colder area or would that make the hall etc too cold. These rooms are all downstairs and that bypass rad sending the heat upstairs to the bedrooms.   In previous houses the bypass was always in a bathroom. 

@david999 I think that setting a thermostat is part and parcel of the radiator balancing process. After all, as you have realised, the ‘stat’ is controlling the whole system based on the temperature in just one area of the whole house / flat / dwelling. My approach was to spend many an enjoyable hour tweaking the radiators so that I achieved a relative balance of heating all throughout the house (doors opened back and heating on 24/7) and having achieved this, then set the thermostat (or at least the node that reports to the Homely controller) to the temperature at which we were most comfortable.

The recommendations I have seen all seem to suggest that the room of choice for the ‘stat is the one you use the longest number of hours per day which in our case, it the sitting room. Our sitting room varies (now it is all set up) between 22.5 and 23.1 degrees C. at various times, the higher end during the early / mid morning when we have some solar gain in the room.   As to open radiator valves, the only valve that ever shuts down (by request) is the old Hive programmable TRV in our bedroom so that we have a cooler room overnight. Nine radiators and a towel rail are all receptive to the heat from the pump and  able to dissipate heat when needed. Regards, Toodles.

@david999

When you refer to a 'stat' associated with radiators, do you mean Thermostatic Radiator Valve (TRV)?

@derek-m yes the wee valves on the side the bypass just has valves with no stats on them

@toodles if we stuck the room stat in the living room the entire house would be cold. In theory if we chucked the room stat in the loft or whacked it up to max and turned all the Trv thingies down then if the bypass radiator was in the cold room areas then all the other rads would shut down and that one rad would never heat that area sufficiently so the rads would turn on to meet needs.  At the minute the room stat is trying to bring the cold rooms up to temp whilst the hall bypass radiator is cooking us, especially if the log burner is running. By the time those rooms are up to temp all the warm areas rad have shut down or not even operated, even upstairs yet the bypass in hall is chucking out heat throughout the day and night . 

@david999  - I think that @derek-m is about to address that point.
and he'll make a better job of it than I will.

The principle is that you don't have room thermostats or TRVs controlling the flow from the heat pump.

You need the ASHP to run continuously, and not switch on/off.
Cycling on/off is energy expensive, and to be avoided.

Yes, you need to use the radiator lockshield valves to 'balance' the flow.
But the TRV's are doing just what you don't want to be happening!

Over to Derek...

@david999 I am feeling a little confused by your various scenarios thus described but it sounds to me as though you are making extensive use of TRV’s on individual radiators - is that right please? The usual way is to start off with all such restrictions removed, i.e., TRV’s opened to max. Or even running without the ‘head’ in place so that you may know the true heating capabilities of each radiator when running fully open without restriction, this would be the starting point. From such a point, you may start restricting the flow (via the lockshield valves, not the trv. at this stage) on the radiators in the hottest rooms. (If you search on this forum for the way to set lockshield valves, you will find advice from a number of contributors.

As you have the additional complication of occasionally employ a log burner, this is something I know not of but would suggest that your initial setting be established without that burner in use as it will introduce more variable! If I have this all wrong, I feel sure another contributor will be along quite soon to correct me and assist you. Regards, Toodles.

@david999

I think that you stated that you are an Engineer, what kind of Engineer? How much do you know about thermodynamics?

@derek-m mechanical electrical. My good friend has two degrees in pumps and gas turbines but not good on heating systems. 

I read the other post and at the minute my heat pump is cycling because of the room stat and in one position too warm leaving rooms cold and the other way in the cold rooms leaving me too warm.  If it was working like a conventional boiler then it would shut down on the room stat providing it’s positioned in the correct place and cycle on demand.. but I’m hearing that perhaps this shouldn’t happen and the pump should run all the time and confused how I would regulate heat. 

Also thinking that if the pump initiated a defrost is the room stat shutting the pump down and causing the ice before it defrosts it